The subject matter disclosed herein relates generally to magnetic resonance imaging (MRI) systems, and more particularly to systems and methods for tuning body coils in MRI systems.
MRI is a medical imaging modality that generates images of the inside of a human body without using x-rays or other ionizing radiation. MRI uses a magnet to create a strong, uniform, static magnetic field (i.e., the “main magnetic field”) and gradient coils to produce smaller amplitude, spatially varying magnetic fields when a current is applied to the gradient coils. When a human body, or part of a human body, is placed in the main magnetic field, the nuclear spins that are associated with hydrogen nuclei in tissue water become polarized. The magnetic moments that are associated with these spins become preferentially aligned along the direction of the main magnetic field, resulting in a small net tissue magnetization along that axis (the “z axis,” by convention) and the gradient coils encode the MR signal.
Radio frequency (RF) coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei, also referred to herein as the Larmor frequency. These RF coils are used to transmit RF excitation signals and receive MR signals used to form the images. Various types of RF coils may be used in an MRI system such as a whole-body RF coils and RF surface (or local) coils. Two common RF coil configurations are the birdcage coil and the transverse electromagnetic (TEM) coil.
At least some known RF coils utilize a plurality of capacitors to tune the RF coil to a desired frequency, e.g., the Larmor frequency. In some cases the RF coil may still not achieve the desired frequency. To achieve the desired frequency, the RF coil is typically removed from the MRI system and at least one of the capacitors may be replaced with another capacitor having a different capacitance. Optionally, capacitors may be added to, or removed from, the RF coil to achieve the desired frequency. The modified RF coil is then reinstalled into the MRI system and the frequency of the modified RF coil is measured to ensure that the RF coil is operating at the desired frequency.
However, the RF coil may need to be retuned several times to achieve the desired frequency. Thus, the for each retuning operation, the RF coil is removed from the MRI system, at least one of the capacitors is replaced with another capacitor having a different capacitance, the RF coil is retested and then reinstalled in the MRI system. Thus, tuning a conventional RF coil is time consuming and may require that the RF coil be removed, modified, and then reinstalled into the MRI system several times, thus increasing the time and cost of tuning the RF coil to the desired operational frequency.